Major depressive disorder (MDD) is a highly prevalent and disabling complication of many diseases and conditions including multiple sclerosis (MS), spinal cord injury (SCI), and traumatic brain injury (TBI). If MDD is effectively identified and treated, significant disability in this population may be prevented or reversed. An important issue for screening for depression, however, is whether or not symptoms such as fatigue, poor concentration and sleep disturbance should be considered in evaluating depressive symptoms. Such symptoms are "trans-diagnostic" in that they could be attributable to MDD, but also could be attributable to the physical and cognitive effects of disorders like MS, SCI, and TBI. We will evaluate large secondary databases of responses to 3 depression measures. We will test the impact of diagnosis on the factor structure of depression responses. In addition, we will apply modern psychometric methods to evaluate, at an item level, whether responses to depression measures differ in persons with a neurologic disorder. As needed, diagnosis- specific cut scores will be developed that account for any differential impact of trans-diagnostic symptoms on the measurement of depression in MS, SCI, and TBI leading to more accurate prevalence estimates of depression, as well as more accurate screening, assessment, and treatment of depression in these patient groups. PUBLIC HEALTH RELEVANCE: Many people who have neurologic conditions like multiple sclerosis, spinal cord injury, and traumatic brain injury also have depression. It can be difficult for clinicians to distinguish symptoms of depression from the symptoms of a neurologic condition and so they may be unsure how to interpret measures of depressive symptoms. The results from the proposed study can lead to increased certainty about diagnosis of depression and less hesitation regarding treatment decisions.